Commit 8795d771 authored Apr 15, 2010 by Frederic Weisbecker

lockdep: Fix redundant_hardirqs_on incremented with irqs enabled



When a path restore the flags while irqs are already enabled, we
update the per cpu var redundant_hardirqs_on in a racy fashion
and debug_atomic_inc() warns about this situation.

In this particular case, loosing a few hits in a stat is not a big
deal, so increment it without protection.

v2: Don't bother with disabling irq, we can miss one count in
    rare situations

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

parent 868c522b

kernel/lockdep.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -2298,7 +2298,12 @@ void trace_hardirqs_on_caller(unsigned long ip)
		return;

		if (unlikely(curr->hardirqs_enabled)) {
		debug_atomic_inc(redundant_hardirqs_on);
		/*
		* Neither irq nor preemption are disabled here
		* so this is racy by nature but loosing one hit
		* in a stat is not a big deal.
		*/
		this_cpu_inc(lockdep_stats.redundant_hardirqs_on);
		return;
		}
		/* we'll do an OFF -> ON transition: */

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